.TH libssh2_sign_sk 3 "1 Jun 2022" "libssh2 1.10.0" "libssh2 manual"
.SH NAME
libssh2_sign_sk - Create a signature from a FIDO2 authenticator.
.SH SYNOPSIS
#include <libssh2.h>
.nf
int libssh2_sign_sk(LIBSSH2_SESSION *session,
                    unsigned char **sig,
                    size_t *sig_len,
                    const unsigned char *data,
                    size_t data_len,
                    void **abstract);

typedef struct _LIBSSH2_PRIVKEY_SK {
    int algorithm;
    uint8_t flags;
    const char *application;
    const unsigned char *key_handle;
    size_t handle_len;
    LIBSSH2_USERAUTH_SK_SIGN_FUNC((*sign_callback));
    void **orig_abstract;
} LIBSSH2_PRIVKEY_SK;

.SH DESCRIPTION
\fIsession\fP - Session instance as returned by 
.BR libssh2_session_init_ex(3)

\fIsig\fP - A pointer to a buffer in which to place the signature. The caller 
is responsible for freeing the signature with LIBSSH2_FREE.

\fIsig_len\fP - A pointer to the length of the sig parameter.

\fIdata\fP - The data to sign.

\fIdata_len\fP - The length of the data parameter.

\fIabstract\fP - A pointer to a pointer to a LIBSSH2_PRIVKEY_SK. See 
description below.

Create a signature from a FIDO2 authenticator, using either the 
sk-ssh-ed25519@openssh.com or sk-ecdsa-sha2-nistp256@openssh.com key 
exchange algorithms.

The abstract parameter is a pointer to a pointer due to the internal workings 
of libssh2. The LIBSSH2_PRIVKEY_SK must be completely filled out, and the 
caller is responsible for all memory management of its fields.

\fIalgorithm\fP - The signing algorithm to use. Possible values are 
LIBSSH2_HOSTKEY_TYPE_ED25519 and LIBSSH2_HOSTKEY_TYPE_ECDSA_256.

\fIflags\fP - A bitmask specifying options for the authenticator. When 
LIBSSH2_SK_PRESENCE_REQUIRED is set, the authenticator requires a touch. When
LIBSSH2_SK_VERIFICATION_REQUIRED is set, the authenticator requires a PIN. 
Many servers and authenticators do not work properly when 
LIBSSH2_SK_PRESENCE_REQUIRED is not set.

\fIapplication\fP - A user-defined string to use as the RP name for the 
authenticator. Usually "ssh:".

\fIkey_handle\fP - The key handle to use for the authenticator's allow list.

\fIhandle_len\fP - The length of the key_handle parameter.

\fIabstract\fP - User-defined data. When a PIN is required, use this to pass in 
the PIN, or a function pointer to retrieve the PIN.

\fIkey_handle\fP The decoded key handle from the private key file.

\fIhandle_len\fP The length of the key_handle parameter.

\fIsign_callback\fP - Responsible for communicating with the hardware 
authenticator to generate a signature. On success, the signature information
must be placed in the `\fIsig_info\fP sig_info parameter and the callback must 
return 0. On failure, it should return a negative number. See
.BR libssh2_userauth_publickey_sk(3)
 for more information.

\fIorig_abstract\fP - User-defined data. When a PIN is required, use this to 
pass in the PIN, or a function pointer to retrieve the PIN.

.SH RETURN VALUE
Return 0 on success or negative on failure.

.SH SEE ALSO
.BR libssh2_userauth_publickey_sk(3)
